Pure Forced Convection Research Articles

Investigation of thermal performance at forced convection in plate-fin heat sink

Interest in studies on more effective and faster heat dissipation in microelectronic equipment has increased in recent years due to the cooling area and equipment size limitations. This study attempts to focus on the effect of different fin geometry parameters on pure forced convection heat transfer. Total surface areas of plate-fin heat sinks were kept constant and were carried out for ten different heat sinks in these analyses. The Ansys-Fluent 2023 R1 commercial package program was used to perform the thermal and hydrodynamic performance analyses. Three-dimensional turbulent forced convection heat transfer analyses at heat sinks were subjected to fluid flow (500≤Re≤3000). The effects of gap between fins, fin thickness, fin height, fin number, and air velocity on the heat transfer and the friction factor were obtained and discussed for heat sinks. It was observed that there was a maximum difference of 0.27 % between the maximum temperatures obtained as a result of this analysis and the experimental study results in the literature. Among the ten cases examined (from Case 1 to Case 10), the highest heat transfer coefficient was obtained in Case 2 (number of fins 6, gap between fins 4 mm, fin height 17 mm and fin thickness 2 mm) at Re = 3000. The heat transfer coefficient of Case 2 was 41.29 % higher than the heat transfer coefficient of Case 4 at Re = 3000; though, the friction factor of Case 2 is 55.93 % higher than Case 4. Also, a useful correlation for the heat transfer coefficient was generated for the fin geometric parameters and Reynolds number.

Experimental and numerical study of mixed convection heat transfer in a vented cavity partially filled with a porous medium: Effects of reynolds and rayleigh numbers on Nusselt number and flow regimes

This article presents a comprehensive investigation of mixed convection flow and heat transfer within a vented, partially side-heated cubical cavity, incorporating a porous medium with low-conductivity square-shaped inclusions. The study encompasses an extensive range of Rayleigh numbers (106 < Ra < 6 × 106) and Reynolds numbers (200 < Re < 4000) while maintaining a fixed Prandtl number of Pr = 0.71. This investigation spans over three decades in Richardson numbers (Ri = Ra/(Re2 Pr)), aiming to discern the interplay between the Nusselt number, Nu, and the Richardson number. Our understanding of Nusselt number dependencies is enhanced by combining PIV measurements of heat transfer and velocity fields with temperature field data. The study uses both experimental and numerical PIV data, incorporating porous media representation to reveal heat transfer scaling with both Reynolds and Rayleigh numbers. Computational Fluid Dynamics (CFD) methods are used to explore the complex physical behavior under different flow conditions. Three distinct flow and heat transfer regimes have been identified, predicated upon the Richardson number. For Ri < 25, the flow structure and Nusselt number exhibit similarities with pure forced convection, where the Nusselt number scales as Nu ∼ Re0.6, independent of the Rayleigh number. Conversely, for Ri > 70, natural convection dominates the vicinity of the heating wall, rendering the Nusselt number less sensitive to Reynolds number variations and predominantly dictated by the Rayleigh number. Notably, the intermediate regime, ranging from 25 < Ri < 70, witnesses a competition between upward-directed natural convection flow at the heating wall and downward-directed forced flow, culminating in a minimum effective Nusselt number.

Effects of non-Darcy mixed convection over a horizontal cone with different convective boundary conditions incorporating gyrotactic microorganisms on dispersion

This paper investigates the influence of dispersion impact on mixed convection flow over a horizontal cone within a non-Darcy porous medium. Multiple convective boundary conditions are applied to address the heat, mass and motile microorganism transfer phenomena. This paper incorporates the dispersion effect for gyrotactic microorganisms due to biological and environmental applications. By imposing appropriate similarity transformations, the nonlinear partial differential equations governing flow, temperature, concentration, and microbe fields are reduced to a system of ordinary differential equations & then solved using the MATLAB BVP4C function. The computation of grid independence test is analyzed for different flow profiles to show the precision of the points. In a few instances, our present numerical data is compared with previously published works, leading to excellent agreement. The non-Darcy effect, as well as mixed convection values from 0.1 to 0.9 and buoyancy parameters from 0.2 to 0.8, all significantly affects the velocity profile. The reduction in the microorganism profile is brought on by the increase in the bioconvection Lewis parameter and bio convection peclet number between 0.3 and 1. In the absence of dispersion, the variation of Biot numbers between 0.5 and 2, favor heat, mass, and motile microorganism transfer the most in the range of mixed convection parameter 0.5 to pure forced convection 1. Thermal, solutal and microorganism dispersion coefficients a, b, c that lie between frac{1}{7} and frac{1}{3} and higher values of modified peclet number ranges from 2 to 10 cause increased dispersion effects which lower flow transfer rates mostly in forced convection regime.

The Role of Mixed Convection and Hydrodynamic Dispersion During CO2 Dissolution in Saline Aquifers: A Numerical Study

AbstractDissolution trapping plays a significant role in CO2 geological storage. When CO2 dissolves in aquifer brines, the aqueous solution is heavier than the underlying resident brine. This results in convective instability in the form of CO2‐rich fingers, which accelerates dissolution. It was recently shown that background flow affects CO2 dissolution by suppressing the development of convective fingers. However, there was a discrepancy between computational results and measurements, with the computational results demonstrating a decrease in the dissolution rate and the laboratory measurements showing no significant effect. Here, we attempted to understand this difference by exploring the relations between the transport mechanisms that facilitate convective mixing. We investigated the role of background flow by using numerical simulations that were validated by laboratory measurements and analytical solutions. Simulations were generated for the same porous medium and fluid pair used in the experiments, keeping the Rayleigh number constant, while changing the background velocity and the Peclet number. Studying the flux components revealed three distinct regimes characterized by the Peclet to Rayleigh ratio Pe/Ra. When Pe/Ra &lt; 0.77, natural convection dominated, and dissolution remained approximately constant. When the background flow was large (Pe/Ra &gt; 2), dissolution was controlled by pure forced convection and increased with Pe/Ra. In the intermediate range (0.77 &lt; Pe/Ra &lt; 2), both natural convection and forced convection were important.

Large eddy simulation of the heat transfer and unsteady pulsation of supercritical carbon dioxide in a square subchannel

In the present study, a large eddy simulation was conducted to study the heat transfer and turbulent flow pulsation of supercritical carbon dioxide (SCO2) in a square subchannel. Three Reynolds numbers of 5385, 13,028 and 18,934 were selected corresponding to the friction Reynolds number (Reτ) of 180, 395 and 550, respectively. Both of the upward flow, downward flow and pure forced convection (g = 0) were covered. Attention was paid to clarifying the effects of flow direction and Reynolds number on the circumferentially nonuniform heat transfer, the cross-sectional velocity redistribution and the macroscopical flow pulsation. It was found that the wall-temperature distribution along the rod circumference is closely related to buoyancy. The heat transfer of the downward flow is superior to upward flow under identical conditions. Besides, the heat transfer of the upward flow is better than that of the forced convection, indicating buoyancy could enhance the heat transfer. In addition, for the upward flow, the cross-sectional velocity is high near the rod gap, but is low at the subchannel center. A quasi-periodic large-scale velocity pulsation was identified near the rod gap. The magnitude of the velocity pulsation is affected by the flow direction, but is independent of the Reynolds number. On the other hand, the dominant frequency of the velocity pulsation increases with increasing Reynolds number, but is unaffected by the flow direction.

Non-linear radiation effect on dusty fluid flow near a rotating blunt-nosed body

A two-phase, dusty boundary-layer flow over an isothermally heated rotating hemisphere is studied for the laminar, incompressible fluid. The contribution of non-linear thermal radiation is analyzed by using the Rosseland diffusion approximation model. The difficulty of having a unified mathematical treatment of the above problem is due to the complex nature of the governing partial differential equations, which arises from the transverse curvature of the round-nosed body, buoyant force, and thermal radiation. Therefore, this study presents a theoretical analysis of a dusty flow and heat transfer over a rotating axisymmetric round-nosed body (for example, hemisphere). In industries, for instance, vehicle industry, blunt-nosed shapes (or round-nosed body) are preferred because it provides better thermal management. The governing equations, along with their appropriate boundary conditions, are numerically solved using the iterative, implicit finite difference method. Numerical solutions are illustrated in the form of streamwise velocity distribution, spanwise velocity distribution, temperature distribution, and skin friction and heat transfer coefficients. The numerical scheme is validated through comparison with the benchmark solutions available in the literature. Solutions obtained here are discussed for i) pure and dusty air and ii) pure and dusty water. A wide range of thermal radiation parameter is tested for the above two cases, and it is found that skin friction coefficient achieves asymptotic behavior for [Formula: see text]; however, heat transfer coefficient increases considerably as much as we strengthen the parameter Rd. Further, momentum and thermal boundary layer thicknesses also increase for [Formula: see text]. Computations are also performed for the buoyancy parameter, λ, ranging from 0 to [Formula: see text], which respectively covers the solution of pure forced convection ( λ = 0) and pure natural convection ([Formula: see text]) boundary layer on a rotating hemisphere.

Conjugate Mixed Convection in a Horizontal Cylindrical Duct under the Solid Shell Internal Heat Generation

This paper deals with three-dimensional, mixed convection in a cylindrical duct horizontally. This latter is partially subjected to a uniform volumetric heat generation at the solid-liquid interface. The working fluid (water) with a parabolic velocity profile and a constant temperature T0 enters the tube. The study was carried out for different Richardson numbers values Ri=0.1-8 at Reynolds number Re=600. Results were conducted so that to show the influence of Richardson number Ri on the dynamic and thermal fields and local Nusselt number Nu(q,z) and peripherally averaged axial Nusselt number Nu(z). Also, analyses of the results showed that the hydrodynamic effects are manifested by the existence of secondary flow, inducing temperature gradient at a cross-section between the top and bottom of the duct. The reversed flow is observed for a low Reynolds number Re=10. A significant increase in heat exchange is observed in mixed convection compared to pure forced convection flow. Correlations for the variation of average Nusselt number Nu (Ri,z) at the entrance region with Ri and z=z¢/Di and local Nusselt Nu(Ri) number in the hydrodynamics establishment zone are proposed and compared with the present numerical results.

Variations in buoyancy-aided turbulent mixed convective heat transfer along a vertical rectangular channel

We performed buoyancy-aided turbulent mixed convection experiments using a vertical rectangular channel heated on one side. To achieve high buoyancy, mass transfer experiments were performed by analogy with heat transfer using a copper electroplating system. Piecewise electrodes were used to measure local mass transfer coefficients along the channel. The Grashof number ranged from 8.05 × 104 to 1.01 × 1010, and the Reynolds number from 985 to 25,450. Local turbulent forced convection correlation was developed based on the correlations of Petukhov et al. and Gnelinski. The local mass transfer rates of mixed convective flow exhibited both impairments and enhancements compared to the rates of pure forced convection, attributable to the effects of buoyancy. Heat transfer of turbulent mixed convection was increasingly impaired with the height of the heated section increased. The Particle image velocimetry (PIV) confirmed the distorted velocity profiles and the redistributed turbulent shear stress.

Investigation of double-diffusive mixed convection effect on the particles dissolution in the shear flow using coupled SPM–LBM

In the present study, double-diffusive mixed convection related to the heat and mass transfer of the solid particles dissolution in a shear flow was numerically investigated. For this purpose, the study employed the combined two-dimensional thermal-concentration smoothed profile-lattice Boltzmann method scheme. The governing equations of the flow, concentration and temperature fields are solved by applying the LBM. The interplay amongst the fluid–solid particle and the boundary condition of the no-slip at the interface of the fluid–solid particle is treated by using the SPM. Initially, a comparison made amongst the results obtained in the present numerical method and to those that had been obtained in the previous works, showing a well compatibility. Then, the impacts of Reynolds number, thermal and concentration Grashof numbers and buoyancy ratio on the flow characteristics and dissolution process have been addressed. Following that, a comparison is made amongst the impacts of pure forced convection and double-diffusive mixed convection on the solid particle dissolution behavior. It is shown that different competitive mechanisms have impact on the migration of the solid particles under the double-diffusive mixed convection; these are the particle mass force, the buoyancy force resulting from the fluid weight, the thermal convection and finally, the concentration convection. The numerical results also revealed the identification of the critical buoyancy ratio, with the dissolution time of the solid particles being sensitive to it.

Aiding and Opposing Re-circulating Mixed Convection Flows in a Square Vented Enclosure

A numerical study is performed to investigate mixed convective flow in a vertically vented square enclosure with heating or cooling one of the vertical walls and the other three walls are insulated. This study is conducted to analyse and clarify the intricate interaction between the buoyancy-induced flow and the pressure-driven external flow in a vertical upward laminar air jet for both assisting and opposing buoyancy situations. The approach of spectral-element that is introduced as a finite-element method with high-order Lagrange polynomials as interpolating functions, is applied to discretise unsteady Navier-Stokes, continuity and energy equations, and for calculating the velocity and temperature fields. The numerical solutions are obtained for air having a Prandtl number of (Pr = 0.7) and for buoyancy parameters which cover the whole mixed convection region, ranging from pure forced convection with a Reynolds number ranging between (10 ⩽Re ⩽350) to pure free convection with a Richardson number ranging between (0 ⩽Ri ⩽30), with a single dimensionless enclosure size. The results reveal that the flow and thermal patterns can be significantly influenced by both aiding and opposing buoyancies. Also, the mean heat transfer rates increase with increasing either the buoyancy force Richardson number or the forced flow Reynolds number in assisting flows. However, in opposing flows, it is found that the mean heat transfer rates decrease with increasing the buoyancy effects for small to moderate (Ri ⩽2) but, they begin rising for higher Richardson number when the free convection starts domination the flow.

Experiments on mixed convection in a vented differentially side-heated cavity filled with a coarse porous medium

This paper reports on an experimental study of mixed convection flow and heat transfer in a vented, differentially side-heated cubical cavity filled with a porous medium consisting of relatively large solid low-conductivity spheres. Rayleigh numbers and Reynolds numbers are varied over the ranges 6 × 106 < Ra < 7 × 107 and 240 < Re < 4250, respectively, for a fixed Prandtl number of Pr = 6.75, thus covering more than three decades in Richardson numbers Ri = Ra/(Re2 Pr). Heat transfer measurements were combined with measurements of the velocity field (using particle image velocimetry) and the temperature field (using liquid crystal thermography) to better understand the dependence of the Nusselt number, Nu, on the Richardson number. We observed three different flow and heat transfer regimes depending on the Richardson number. For Ri < 10, the flow structure and the Nusselt number scaling are similar to those for the pure forced convection, i.e., the Nusselt number scales as Nu ~ Re0.61 independent of Rayleigh number. For Ri > 40, natural convection dominates the flow in the vicinity of the heating wall. The Nusselt number becomes less sensitive to the Reynolds number and is mainly determined by the Rayleigh number. In the intermediate regime for 10 < Ri < 40, the upward directed natural convection flow at the heating wall competes with the downward directed forced flow leading to a minimum effective Nusselt number. A Nusselt number correlation is derived that is valid in the range 0.1 < Ri < 100 covering all three regimes.

Numerical study of evaporation assisted hybrid cooling for thermal powerplant application

Abstract. This paper describes a numerical study of the effect of evaporative cooling on forced convective heat transfer in a system experiencing combined heat and mass transport. A multi-dimensional mathematical model has been developed to conduct simulations over a range of operating parameters to acquire insight into the dual mode cooling where convective heat transfer is augmented by evaporative heat and mass transfer process. The system being modeled consists of a thin liquid water film that undergoes evaporation as a result of being exposed to a prescribed heat flux and laminar convective flow condition. Predictions from the simulations indicate that in comparison to pure forced convection cooling, under convective-evaporative hybrid cooling conditions the overall heat transfer coefficient is increased by a factor of ~4 to 5, where evaporation alone contributes to 80−90% of the overall performance. A critical Reynolds number has been found beyond which no significant enhancement in the overall heat transfer is observed. Numerical results also identify a critical film thickness beyond which the thermal inertia across the liquid film becomes dominant and starts to suppress the overall heat transfer process. System size requirements and water consumption of hybrid cooling for power plant applications are compared with conventional water, and air- cooled systems and was found to be significantly lower.

Numerical investigation of flow and combined natural-forced convection from an isothermal square cylinder in cross flow

Unsteady flow and heat transfer from a horizontal isothermal square cylinder is studied numerically using a three-dimensional computational model to investigate the influence of buoyancy on the forced flow and heat transfer characteristics. The numerical model is based on a horizontal square cylinder subjected to laminar fluid flow in an unconfined channel. The governing equations in 3D form are solved using a fractional step method based on the finite difference discretization in addition to a Crank–Nicholson scheme employed to the convective and the viscous terms. Two working fluids–air (Pr = 0.7) and water (Pr = 7)–are considered, and the flow and heat transfer simulations were carried out for the Reynolds and Richardson numbers in the intervals 55 ≤ Re ≤ 250 and 0 ≤ Ri ≤ 2, respectively. The flow characteristics such as time-averaged drag/lift, rms drag/rms lift coefficients as well as Strouhal number were computed. The heat transfer from the cylinder is assessed by mean Nusselt number (and rms Nusselt number) over the total heated cylinder walls. As the buoyancy increases, the mass and the velocity of the fluid flowing underneath the cylinder increases. The fluid is injected into the near wake region with an upward motion which significantly alters the flow field in the downstream as well as upstream regions. The effects of Reynolds, Richardson and Prandtl numbers on the flow field and temperature distributions are discussed in detail. It is shown that the flow and heat transfer characteristics are influenced more for air than water. To fill the void in the literature, useful empirical correlations of practical importance are derived for pure forced and pure natural as well as mixed convection. The mixed convection correlations, in terms of the ratio of pure forced convection, are also developed, and their implications are discussed.

Comparison of empirical models with an experimental database for condensation on banks of tubes

Empirical models for calculating the heat-transfer coefficients for condensation on banks of tubes were compared with the experimental data set obtained by the various previous investigators consisting more than 4000 data points for 6 different condensing fluids and 13 different tube bank configurations. All the banks considered in this study, involved the condensation of the pure vapours, the exceptions are that of the Briggs and Sabaratnam (2003) and Shah (1978, 1981), since their pure vapours consisted of incondensable air. For the forced convection flow region (F < 3.5), it was observed that some of the data were underpredicted by the recent models, recommending that the effect of the shear stress due to high vapor velocity overcomes the effect of the inundation on the heat transfer rate while vice versa is the case for the models overpredicting results. Similarly, for the free convection flow region (F > 3.5), it is suggested that the data overprediction by some of the models was due to the boundary layer separation and inundation effects, whereas the data underprediction was due to the generation of the turbulence within the condensate film due to high velocity on the condensate film. The inclusion of the inundation effect to a pure forced convection model of Shekriladze and Gomelauri (1966) as recommended by Cipollone et al. (1983) lead the model of Cavallini et al. (1985) to be the most accurate model compared to the other models for steam only. It was found that the Fujii and Oda model (1986) is the most accurate model among the empirical models been demonstrated in this paper, giving an agreement with the experimental data base to within an average absolute of the errors of about 21.5%. It accounts for the effects of the shear stress on the surface of the film condensate and the inundation within the bank.

Experimental determination of heat transfer in a Poiseuille-Rayleigh-Bénard flow

This paper deals with an experimental study of heat transfer in a Poiseuille-Rayleigh-Benard flow. This situation corresponds to a mixed convection phenomenon in a horizontal rectangular channel uniformly heated from below. Flow visualisation and temperature measurements were achieved in order to describe the flow regimes and heat transfer behaviour. The classical measurement techniques such employing thermocouples give local measurement on one hand and on other hand they often disturb the flow. As the flow is three-dimensional, these techniques are not efficient. In order to not disturb the flow, a non-intrusive method is used for thermal measurement. The Planar laser Induced Fluorescence (PLIF) was implemented to determine thermal fields in the fluid. Experiments conducted for various Reynolds and Rayleigh numbers allow to determine the heat transfer and thus to propose correlation for Nusselt number for a mixed convection flow in Poiseuille-Rayleigh-Benard configuration. First a description of the use of this technique in water flow is presented and then the obtained results for various Reynolds and Rayleigh numbers allow to propose a correlation for the Nusselt number for such configuration of mixed convection. The comparison between the obtained heat transfer and the pure forced convection one confirms the well-known result that the convective heat transfer is greatly enhanced in mixed convection. Indeed, secondary flow induced by buoyant forces contributes to the refreshment of thermal boundary layers and so acts like mixers, which significantly enhances heat transfer.

Non-linear interaction of buoyancy with von Kármán’s swirling flow in mixed convection above a heated rotating disc

In this paper, a systematic computational and theoretical study of the thermo-fluid-dynamics governing the flow above a heated horizontal rotating disc is presented. The fluid flow field is much more complex here as compared to von Kármán’s original solution (which took into account only the effect of disc rotation), and the effects of non-linear interaction between buoyancy and rotation are critically analysed here by studying the separate and combined roles of disc rotation and buoyancy on the fluid dynamic and heat transfer characteristics. The self-similarity of von Kármán’s flow field is lost, and the present paper establishes, for the first time, that the flow field above a heated rotating disc is divided into three distinct fluid dynamic regions. The three regions are demarcated by the loci of V̂z=0 and V̂r=0. In region 1 (R-1), V̂r is positive and V̂z is negative (such directions of the velocity components are characteristic of von Kármán’s flow or pure forced convection). In region 2 (R-2), V̂r is negative and V̂z is positive (such directions of the velocity components are characteristic of pure natural convection near a static disc surface). In region 3 (R-3), both V̂r and V̂z are negative. The forced convection results are obtained asymptotically at a large non-dimensional radius R within the region R-1 showing the dominance of forced convection mechanism, however, the fluid retains the signature of natural convection even at large values of R in the region R-3 where there is an inward radial velocity. Similarly, although a plume forms in the central portion of the disc where the solution is dominated by the effects of buoyancy, the fluid retains a signature of the disc rotation in the helical pathlines of fluid particles rising in the plume (whereas there is no swirl velocity present in pure natural convection above a static disc). The non-linear interaction between buoyancy and rotation results in several peculiar, rather non-intuitive, flow phenomena. Examples of such peculiarity include (i) the presence of a very sensitive spot on the upper boundary such that for a small change in this initial position the fluid pathlines may face drastically different final outcomes, (ii) the presence of a small portion near the centre of the disc where the fluid supplies energy to the disc, (iii) the effect of rotation on the rate of convective heat transfer being diminished by buoyancy over certain part of the disc while being enhanced over another part. This non-linear effect on Nusselt number is quantified here in terms of a Grashof number defined for mixed convection (Grmc).

Numerical study on the heat transfer characteristics of filled-type solar collector with U-tube

In this paper, the heat transfer characteristics of individual filled-type evacuated solar collector with U-tube is investigated by three-dimensional numerical method. The effect of thermal conductivity of the heat transmission component, mixed convection and the inlet velocity of working fluid on heat transfer characteristics of filled-type collector tube are analyzed. And the thermal performance comparisons between the filled-type collector tube and U-tube evacuated tube solar collector is also made. The results show that the temperature distribution and the heat transfer characteristics of the filled filled-type collector tube are affected remarkably by these factors. Under the action of buoyancy force, the temperature of the heat transmission component can be reduced compared with the pure forced convection, but the heat gain of working fluid is not increased. With increase of the thermal conductivity, the total heat gain of collector tube increases slightly when thermal conductivity of the heat transmission component is lower than 5W/(mK), but the total heat gain of collector tube changes little once the thermal conductivity is above this value. The thermal efficiency of filled-type collector tube is 6% higher than that with copper fin. And the surface temperature of the absorber tube can reduce 40°C, which indicates the filled-type collector tube has a favorable thermal performance.

3D Fully Developed Laminar Mixed Convection in Horizontal Concentric Annuli with the Presence of Porous Blocks

This paper reports the results of a numerical investigation to examine the potential of a four porous blocks inserted specifically for augmenting heat transfer from the inner heated wall of concentric horizontal annuli. Results are presented for a range of the values of the Grashof number, for two value of the Darcy number and for three value of the Prandtl number. Results are presented in the form of contours plots of the streamlines and for the temperature isotherms, and in terms of the overall heat transfer coefficients and friction factor. The average Nusselt number ( b N u ) increases significantly with an increase of the Grashof number and the Prandtl number ( Pr ). For pure forced convection, b Nu is independent of P r . With the use of the four porous blocks, the friction factor is consequently increased compared with the situation without porous blocks. The decrease of the Darcy number leads to an increase of the friction factor. If the fully fluid case is taken as a reference, the use of porous blocks is justified only when the ratio of the average Nusselt number to the friction factor is enhanced. At 3 10 Da − = , the enhancement

Onset of the Mutual Thermal Effects of Solid Body and Nanofluid Flow over a Flat Plate Theoretical Study

The falling and settling of solid particles in gases and liquids is a natural phenomenon happens in many industrial processes. This phenomenon has altered pure forced convection to a combination of heat conduction and heat convection in a flow over a plate. In this paper, the coupling of conduction (inside the plate) and forced convection of a non-homogeneous nanofluid flow (over a flat plate) is investigated, which is classified in conjugate heat transfer problems. Two-component four-equation non-homogeneous equilibrium model for convective transport in nanofluids (mixture of water with particles<100nm) has been applied that incorporates the effects of the nanoparticles migration due to the thermophoresis and Brownian motion forces. Employing similarity variables, we have transformed the basic non-dimensional partial differential equations to ordinary differential ones and then solved numerically. Moreover, variation of the heat transfer and concentration rates with thermal resistance of the plate is studied in detail. Setting the lowest dependency of heat transfer rate to the thermal resistance of the plate as a goal, we have shown that for two nanofluids with similar heat transfer characteristics, the one with higher Brownian motion (lower nanoparticle diameter) is desired.

Effects of rotation on the trailing vortex and heat transfer from a horizontal rotating cylinder at higher Grashof number

In the present study, effects of rotation on the trailing vortex and heat transfer from a large diameter horizontal rotating cylinder in still air have been experimentally investigated whereas earlier studies considered cylinders with smaller diameters. As the rotational speed n is increased, the trailing vortex would deflect in the rotational direction, the flow state of air near the cylinder would vary from laminar to turbulent, the heat transfer would transit from pure natural convection to mixed convection, and finally to pure forced convection resulted from rotation, the trailing vortex would break down and disappear. The variation of deflection angles ω with the parameter Rer/Gr can be expressed as w=32.3Rer/Gr at lower rotational speed. The discriminant to determine the disappearance of trailing vortex can be presented as Rer2/Gr=7.51.